It is known to use plastic containers in the food preparation and restaurant industry to package prepared foods. The typical food container of the prior art consists of a clear or solid colored base and a clear lid. In order to maintain the quality of food contents and prevent tampering with the contents of a sealed container, it is desirable that the food container, once initially sealed, not be capable of being initially opened without visible indication of the container having been opened. To achieve this feature, container manufacturers have designed containers having integral tamper evident features. Typically, these containers consist of a lid that is hingedly attached to a base. The lid seals to the base by superposing the rim of the lid upon the rim of the base or inserting the lid rim within the confines of the base rim. These types of plastic containers are sold as one-piece containers and are often referred to as “clamshell” containers or packages.
There are several general types of tamper evident clamshell food containers. One type involves utilizing a tear-away or break-away mechanism at the sealing side (non-hinged side) of the container. In this type of container the lid and base each have interlocking elements respectively located on or near the lid, rim and base rim where the two rims meet when the container is sealed (i.e. at a non-hinged side or portion of the container). The interlocking element of the lid or base is conventionally located on a tab or flange extending from the rim of the lid or base. Either or both of the tabs are attached to their respective rims by a frangible section of plastic. When the lid and base are placed in initial sealing arrangement, the interlocking elements on or near the lid rim and base rim engage and lock together. In order to open the initially sealed container, the frangible section of one or both tabs must be ruptured so as to release the tab or tabs from the container. Because the interlocking sealing elements are located on the tabs, rupturing one or more tabs from the container disables the locking mechanism. The ruptured tab provides evidence of the container having been opened. One shortcoming with the prior art food container described above is that the interlocked tabs can be cut from the container in clean fashion using scissors or another cutting implement so as to remove any indicia of the container having had a tamper evident mechanism.
Other types of clamshell containers incorporate the tamper evident mechanism as part of the structure that forms or includes the hinge. In these containers, the container is designed to require a severance near the hinge in order to unseal (initially open) the container. This construct make the hinge a single use hinge. These types of hinges often utilize some type of tear strip or tab lifting mechanism to rupture the hinge area. In other cases, the hinge structure is adapted to break by application of a squeeze force that causes the relative movement of two adjacent sides (the top flange and the vertical span of material) that form the hinge arrangement. The various hinge rupturing mechanisms are typically complex requiring intricate geometry and forming to make the container. Also due to the large span between the lid flange and base flange, additional amounts of plastic are needed to form the container. Containers with tear strips and break-away tabs are also ecologically unfriendly and present disposal issues for the consumer. In this respect, after rupturing the tamper-evident seal the user is left with a piece of plastic that needs to be separately discarded from the remaining container. There is thus a need in the art for a re-closable plastic food container that is easy for end consumers to operate; combines reliable tamper evidence and defense against prying intrusion; and that uses a minimum of material to manufacture.